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Full text of "The Morphology And Evolution Of The Apes And Man"

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THE  MUSCULAR  SYSTEM                  1ST
tendinous thread given off from the tendon of the flexor profundus indicis. In the Gibbons it is a small, but distinct muscle.
In the Apes the conditions of the flexor longus pollicis and flexor profundus digitorum represent stages in the evolution of the arrangements present in Man. In lower animals the flexor mass is divisible into radial, u3nar and condylar parts. In the Apes and Man the condylar part forms the flexor sublimis digitorum, and the radial and ulnar parts form the deep flexors. The deep flexor mass undergoes vertical cleavage, the line of splitting moving medio-laterally in zoological order. In the Gibbons the division is such that the tendons for the annularis and minimus lie to the ulnar side, and those for the pollex. index and rnedius to the radial side of the cleavage line. In the higher Simiidae the tendon for the medius also lies to the ulnar side, and the tendons for the pollex and index are placed on the radial side of the cleavage line. In Man the tendon for the pollex is split off and those for the other digits combine to form a true flexor profundus digitorum.
Lumbricales.—In the Chimpanzee the first and second muscles arise from the radial sides of separate tendons of the flexor profundus ; and in one animal they -were connected by a muscular slip. The third rose from two flexor tendons, and the fourth sprang from the ulnar side of the deep flexor tendon of the ring finger. In the Gorilla the first and fourth lumbricals arise from single tendons, but the second and third each arise from two flexor tendons. In the Gibbons and Orang the principle is similar to that in the Chimpanzee, The insertions in all Apes are as in Man.